The present invention relates to a gear arrangement for alternately actuating two reading/writing units for chip cards, these units being arranged essentially in one plane in a tachograph, for the purpose of transporting a respective chip card into the withdrawal position, having a servomotor, of which the direction of rotation can be reversed, and a control slide, which is in operative connection, in terms of gearing, with the servomotor.
Tachographs of the generic type are generally designed as built-in devices with a flat, cubical built-in housing. A very small amount of installation space is thus available for the reading/writing units and the drive means, which cause the chip cards which are located in the reading/writing position, and are locked in this state, to be moved into the withdrawal positions. On the other hand, chip cards which are deformed, i.e. become curved or corrugated, during use require a considerable amount of force in order for it to be possible for them to be moved into the withdrawal position. However, cost limits and the fact that there is a considerable shortage of space on the format-filling printed circuit board, in respect of the housing of the tachograph, mean that, rather than it being possible for each reading/writing unit to be assigned a servomotor, a single servomotor has to be provided for the two reading/writing units, this single servomotor being controlled in a suitable manner and, with the interposition of a gear arrangement which deflects the force flux, alternately causing one chip card or the other to be transported into the withdrawal position.
The restrictive conditions mentioned above, of course, also influence the selection of the servomotor in respect of its power, it being possible for the torque requirement which has to be met by the servomotor to be reduced by a high gearing-related reduction ratio being provided between the servomotor and the actuating members assigned to the reading/writing units. This results in a possibly unreasonably long waiting period as a chip card is being discharged, and requires increased gearing outlay with correspondingly large amounts of space being required.
A gear arrangement which is known in this context from DE-U-200 15 100.2 provides means in the form of a wedge mechanism between a control slide, which is driven by a servomotor, and the carriages, which are mounted in the relevant reading/writing units and are assigned to the chip cards, in order to deflect the movement of the control slide in the discharge direction of the chip cards. Such a drive connection, on account of high frictional losses and as a result of transverse forces and the system-induced division of forces, requires increased power of the servomotor and, as a result of the necessary guidance accuracy of the components on which the wedge-mechanism elements are formed, gives rise to very high production outlay.